Recovery of carbon dioxide



G. T. REICH RECOVERY OF CARBON DIOXIDE Jan. 3,' 1939.

Filed Feb. 16, 1938 To @SOME TEE ii-W Patented Jan. 3, 1939 y 1, 2,142,917

UNITED STATES PATENT OFFICE RECOVERY F CARBON DIOXIDE Gustave T. Reich, Philadelphia, Pa.

Application February 16, 1938, Serial No. 190,860

14 Claims. (Cl. 23-150) This invention relates to the recovery of carlarly the medicinal grades of mineral oil, are esbon dioxide and particularly to an improved pecially suitable for use in the process of the inmethod of recovering carbon dioxide from gases vention. containing this substance by absorbing the car- In order to illustrate the principles of the inbon dioxide in alkali carbonate solutions and devention, a method of recovering carbon dioxide 5 composing the alkali bicarbonate thus formed by from `flue gas with a sodium carbonate solution heat. embodying the invention will be specically de- A principal object of the invention is the proscribed with reference to the accompanying vision of a method whereby the recovery of cardrawing showing a diagrammatic low sheet of bon dioxide may be effected more eiiiciently, with such a process. 10 lower heat expenditure and smaller space reiThe absorber contains a solution of sodium quirements than heretofore. carbonate through which ue gas containing carift has been found that the amount of heat bon dioxide is passed. The concentration ofthe required to decompose alkali bicarbonates in solid sodium carbonate and its time of passage through liorm is much less than that required to .fdethe absorber are such that a substantial amount 15 compose these substances in solution. Furtherof solid sodium bicarbonate is formed therein. lrnfore since the rate of decomposition is much In order to insure the formation of solid sodium greater in the solid form, and the bulk is much bicarbonate, the solution should contain at least smaller, the size of the apparatus required :for 12 parts of Sodium Carbonate to each 100 parts a given production of carbon dioxide is very of. water. The residual gases pass out ofthe 20 greatly reduced. However, the handling of solid top of the absorber to waste and the suspension alkali bicarbonates is mechanically diiicult and of sodium bicarbonate is drawn off at the boteexpensive in labor requirements and is to be tom to a filter or other separating device. avoided as far as possible. In the lter, a thick slurry or paste of solid I have found that the high heat economy resodium bicarbonate is separated from the mother 25 siding in the dissociation of solid alkali bicarliquor, COmprSng a Saturated solution of sobonate may be retained, together with all 0f the dium bicarbonate which will normally contain important advantages and economies of handling greater or less amounts of sodium carbonate. only fluid materials, by carrying the carbonation The bicarbonate is then advantageously mixed of the alkali carbonate solution beyond the point with enough 0f the inert liquid, fOr eXample, an 30 of separation of solid alkali bicarbonate, sepequal Volume oi rened high-boiling mineral oil, arating the solid bicarbonate and suspending it so that any air or undissolved gas contained in an inert liquid medium, wherein it is distherein will be released in the deaerator. The sociated by heating into carbon dioxide and temperature of the mixture should not be thigh ,alkali carbonate. The solid alkali bicarbonate enough to effect any substantial dissociation of 35 when mixed with the inert liquid may be assothe sodium bicarbonate during the deaeration. ciated with suflicient water sothat the alkali The deaerated mix is then passed into the decarbonate resulting from the dissociation will composer, together with a further amount of oil largely or entirely dissolve therein, but preferwhich has been heated to the dissociation temably the sodium bicarbonate is dewatered as far peratureofsodiumbicarbonate or preferably above 40 as is possible by filtration, centrifuging or the this temperature. .In the decomposer, additional like, and water, or solution separated from .the heat may be supplied if necessary, through a suspended bicarbonate, is added to the mixture jacket or heating coils, to effect the complete, or of oil and carbonate to dissolve the carbonate so substantially complete, dissociation of the so- Athat the separation of the alkali carbonate from ,dium bicarbonate into sodium carbonate and 45 the inert liquid and its return to the carbonation carbon dioxide. The sodium bicarbonate disoperation is simple and easy. sociates readily at to 105 C. The oil may be The liquid medium should be inert to, and a preheated up to, for example, to 200 C. or non-solvent for, alkali carbonates and bicarbonhigher, so that all or av substantial portion ofthe 50 4ates at the temperature of dissociation and heat of dissociation is supplied in this manner. 50 immiscible with water. It should have a low The carbon dioxide is drawn off to a holder, volatility' at 100 C. and for the use in the rewhile the residual mixture of oil, sodium carcovery of carbon dioxide for the production of bonate, and more or less water, according to the dry ice, it should be odorless and tasteless. water content of the sodium bicarbonate slurry 5a gI-Iigh-boiling liquid hydrocarbons, and particuoriginally mixed with the oil, is mixed in the dis- 55 solver with suiiicient mother liquor from the bicarbonate separation operation to completely dissolve the sodium carbonate. The sodium carbonate solution is separated from the oil in the decanter and is returned to the absorber, being heated or cooled, if necessary, to the desired temperature for the absorption.

The oil separated in the decanter is returned, in part, to be directly mixed with the sodium bicarbonate solution, and in part to the heater to be reheated for reuse in the decomposer. It will be seen that in the process described there is a continuous recirculation of oil through the right-hand side of the system and a continuous recirculation of alkali through the left-hand side of the system, with practically no opportunity for loss. The only material which has to be added to the system is the very small amountvof water which passes out of the decomposer with the carbon dioxide.

Although the system of operation described for the purpose of illustration oiers many advantages of operation, the invention is not limited to this particular system as many variations in arrangement and method of operation may be made Without departing from the principles of the invention. Other high-boiling, inert liquids having the properties hereinbefore outlined may be used in place of mineral oil, and potassium carbonate may be used alone or in admixture with sodium carbonate as the absorbing agent. The oil added to the bicarbonate in the decomposer, or as it is fed to the decomposer, may be heated to a suflicient temperature to effect practically complete dissociation of the bicarbonate or a substantial proportion of the heat may be supplied to the mixture in the decomposer.

I claim:

1. In the production of carbon dioxide by the thermal dissociation of alkali bicarbonate, the improvement which comprises suspending the bicarbonate in a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates during the dissociation.

2. In the production of carbon dioxide by the thermal dissociation of alkali bicarbonate, the improvement which comprises suspending solid bicarbonate in a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates during the dissociation.

3. In the production of carbon dioxide by the thermal dissociation of alkali bicarbonate, the improvement which comprises suspending the bicarbonate in a high-boiling mineral oil during the dissociation.

4. In the production of carbon dioxide by the thermal dissociation of alkali bicarbonate, the improvement which comprises suspending the bicarbonate in a high-boiling mineral oil during the dissociation, and supplying a substantial portion of the heat of dissociation by preheating the mineral oil.

5. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate With a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates, and thermally decomposing the alkali bicarbonate into carbon dioxide and alkali carbonate while it is mixed with said liquid.

6. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling mineral oil, and thermally decomposing the alkali bicarbonate into carbon dioxide and alkali carbonate While it is mixed with said liquid.

7 A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling mineral oil, and thermally decomposing the alkali bicarbonate into carbon dioxide and alkali carbonate while it is mixed With said liquid, a substantial portion of the heat of dissociation being supplied by preheating the mineral oil before mixing it with the alkali bicarbonate.

8. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling inert liquid immiscible With aqueous solutions of alkali carbonates, thermally decomposing the al* kali bicarbonate into carbon dioxide and alkali carbonate while it is mixed with said liquid, adding liquor separated from the alkali bicarbonate to the resulting mixture of inert liquid and alkali carbonate, and separating the aqueous liquor from the inert liquid.

9. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates, thermally decomposing the alkali bicarbonate into carbon dioxide and alkali carbonate While it is mixed with said liquid, adding liquor separated from the alkali bicarbonate to the resulting mixture of inert liquid and alkali carbonate, separating the aqueous liquor from the inert liquid, and subjecting the liquor to the further action of carbon dioxide-containing gases.

10. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate With a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonate, thermally Idecomposing the alkali bicarbonate into carbon dioxide and alkali carbonate While it is mixed with said liquid, adding liquor separated from the alkali bicarbonate to the resulting mixture of inert liquid and alkali carbonate, separating the aqueous liquor from the inert liquid, and mixing the separated inert liquid from further solid alkali bicarbonate,

11. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates, thermally decomposing the alkali bicarbonate into carbon dioxide and alkali carbonate while it is mixed With said liquid, adding liquor separated from the alkali bicarbonate to the resulting mixture of inert liquid and alkali carbonate, separating the aqueous liquor from the inert liquid, heating the separated liquor, and mixing it with further solid alkali bicarbonate.

12. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates, deaerating the mixture, and subjecting the mixture to a temperature at which the alkali bicarbonate is dissociated into carbon dioxide and alkali carbonate.

13. A method of recovering carbon dioxide Which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate With a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates, deaerating the mixture, adding a further portion of the inert liquid to the mixture, and subjecting the mixture to a temperature at which the alkali bicarbonate is dissociated into carbon dioxide and alkali carbonate.

14. A method of recovering carbon dioxide which comprises passing a gas containing carbon dioxide through a solution of alkali carbonate until solid alkali bicarbonate is formed, separating the solid alkali bicarbonate, admixing the separated alkali bicarbonate with a high-boiling inert liquid immiscible with aqueous solutions of alkali carbonates, deaerating the mixture, and adding to the mixture a further portion of the inert liquid which has been preheated to a temperature sufficient to raise the mixture to a temperature at which the alkali bicarbonate is dissociated into carbon dioxide and alkali carbonate.

GUSTAVE T. REICH. 

